1. Technical Field of the Invention
The present invention relates to a whole-body plethysmograph having calibration of the pressure gauge, comprising an air tight, lockable cubicle for the reception of a person to be examined, a cubicle-pressure pressure gauge that responds to the interior pressure of the cubicle, a mouthpiece with a valve, by means of which the respiratory flow can be barred and a closure-pressure pressure gauge connected to the mouthpiece to measure the pressure in the mouth of the person, as well as an evaluation unit connected to both pressure gauges.
2. Description of the Prior Art
A plethysmograph is known in the art as an apparatus for measuring the changes in the volume of an organ or a part of the body. The whole-body plethysmograph serves especially well to measure changes in the volume of the thorax-lung system. Various examination methods are possible and are often combined. One known method consists of measuring the interior pressure of the cubicle and the respiratory flow rate, whereby conclusions can be drawn about the alveolar pressure and the bronchial airway resistance. Another method consists of measuring, with barred respiratory flow, both the pressure in the thorax-lung system, as well as in the cubicle. The patient breathes voluntarily against the closure and, thus, changes his lung volume. With knowledge of the gas laws, important results can be determined from the measured fluctuations in pressure. Thus, the residual volume of the lung (thoracal gas volume) can be defined.
A major drawback with plethysmography concerns accurately calibrating the pressure absorber, both at the mouth of the test person as well as in the chamber. An exact calibration and adjustment is required because the relative pressure differences are very small and, therefore, possible disturbing influences must be eliminated. It is, therefore, possible that the pressure gauge has a specific frequency dependency. The methods used by the prior art for calibration are inexact, laborious and complicated and could frequently not be executed by the medical operating personnel in a satisfactory manner. Here calibration of the closure-pressure pressure gauge was effected in a static manner by means of a constantly specified pressure and, thus, fully independently of the cubicle-pressure calibration.